Conventional filter apparatus utilized in machine tool operations of the type described in U.S. Pat. Nos. 4,507,061 and Re. 32,135 separate machine tool chips and other contaminants from coolant so that clean coolant may be returned to the machine tools for reuse. Often times, the contaminants are very small and of an elongated shape. Usually one or more horizontally disposed filter drums are located adjacent the bottom of a settlement tank. A suction is provided by a pump to the interior of the filter drum to pull coolant through the filter element to move the coolant from one side of the filter to the other. Filter cake, comprised of small chips and other contaminants, is formed on the outside of the drum surface. The drum is periodically indexed to enable a doctor blade to scrape off a portion of the accumulated filter cake, which drops to the bottom of the tank for removal by a dragout conveyor.
The conventional filter element is comprised of a continuous length of wedge shaped wire wrapped around a drum-shaped support. The filter element thereby includes elongated openings through which some elongated contaminants are allowed to pass if the contaminants are aligned in the direction of fluid movement as they strike the filter. The passage of these elongate contaminants allows the contaminants that pass through the filter to be recirculated to the machine tools.
An alternate type filter system that has been tried is fabricated from rectilinear mesh, wire cloth or the like. Although the minute square openings formed by the woven wire cloth are effective in preventing the passage of elongate contaminants, the surface is not a flat planar surface and thus becomes clogged when scrape cleaning is attempted.